This invention relates generally to the art of film wrapping systems for use in wrapping objects with shrink wrap film and more particularly to improvements directed to making a side seal in the film.
A wide variety of systems are known for wrapping packages in thermoplastic film. Typical thermoplastic films utilized in such shrink wrap packaging systems include polyolefin, PVC and LDPE. More recent machines for wrapping packages in thermoplastic film utilize a continuous longitudinal or side sealer and an end sealer which moves at approximately the velocity of the packages as they travel through the machine so that it is not necessary to stop the packages while performing the end sealing operation.
One type of continuous side seal mechanism utilizes an elongate heated wire oriented in the direction of travel of the packages to heat and weld film plies and subsequently separate excess plastic film from the package. A variant of this type of side seal mechanism employs a fixed blade to heat and weld film plies, which simultaneously may cut the excess or waste film away from the welded seam. Another type of side sealing mechanism commonly utilized in shrink wrap packaging systems utilizes upper and lower rotating rollers or elements between which the plies of the film pass to form the weld. These rotary wheel side seal mechanisms employ a single mechanism to perform the dual operations of sealing the two plies of film together to form the weld and cutting the film to separate the excess selvage film outboard of the weld.
Side seal mechanisms of these and other prior art designs typically produce a relatively thick or wide seal on the wrapped package. One advantage of covering products in shrink wrap film is that the wrapping completely envelops the product without distracting from the aesthetic appeal of the package. Retailers and consumer product manufacturers desire packaging that does not interfere with nor detract from the product. A thick or wide side seal is therefore viewed as undesirable, particularly for low profile packages such as audio compact disc packages where the side seal is positioned on the thin side or height of the CD case.
Additionally, each of these prior techniques requires very high temperatures of the sealing mechanism to accomplish both the welding and separation functions. Typically, temperatures on the order of 500° F. or greater are required to heat the film to a molten state for separation of the selvage from the package.
Thus, while prior side seal mechanisms are seemingly simple, they require significant and complex maintenance efforts to maintain proper operation. The high temperatures required for separation of the selvage film results in sputtering of the molten film onto the components of the side seal mechanism. Such an accumulation of molten film or thermoplastic material on the heated welding or cutting mechanism may interfere with efficient heat transfer resulting in inferior weld formation and cutting operation. Additionally, the constant rubbing of the film on the cutting mechanism rubs off a coating on the cutting mechanism intended to increase thermal efficiency. Moreover, as a result of this inferior performance, the side sealer components must typically be serviced or repaired at least weekly and often daily.
Additionally, other complicating factors are involved in the servicing of these known side sealer mechanisms, which lead to extended service times. First there is an increased down time to allow for cooling of the system components. Moreover, these prior systems have relatively complicated disassembly and reassembly procedures to remove the film deposited on the components and maintain their serviceability. Finally, critical and detailed calibration and adjustment are required each time the side seal mechanism is broken down, cleaned and reassembled.
Therefore, a need exists in the shrink wrap packaging industry for a side seal mechanism which can readily accommodate a wide variety of film materials and repeatedly and consistently produce a thin, narrow, clean and accurate side seal weld and separation of the selvage material without the demanding service and maintenance requirements associated with known side seal mechanisms.